Method of enameling strips and sheets of steel

ABSTRACT

A multi-stage method of providing work pieces, especially bands, strips, and sheets with a layer of enamel, according to which the work piece to be enameled is degreased and subsequently subjected to a plurality of treatment steps with a rinsing step being effected after each treatment step, said method including descaling the work piece in a nitric acid of from 3 to 8 percent by volume, electrodepositing from at least one electrolyte bath within a temperature range of from room temperature to 80*C upon the thus treated work piece a metallic layer containing iron and at least one of the metals, nickel, cobalt and manganese, in which at least one of the metals nickel, cobalt and manganese up to a total concentration of from 50 grams per liter of these foreign metals, posttreating the work piece in an acid within a time period of from 10 to 20 seconds, and subsequently enameling the work piece.

United States Patent [1 1 Sieckmann et al.

[73] Assignee: Hoesch Aktiengesellschaft,

Dortmund, Germany [22] Filed: Apr. 7, 1971 [21] Appl. No.: 132,195

[30] Foreign Application Priority Data Apr. 9, 1970 Germany P 20 16 989.5

[52] US. Cl. 204/38 C, 204/45, 204/48,

204/49, 204/ 146 [51] Int. Cl. C23f 17/00, C23b 5/08, C23b 5/30 [58] Field of Search 204/38 R, 38 C, 45, 204/48, 49, 146

[56] References Cited UNITED STATES PATENTS 3,227,637 1/1966 De Hart 204/38 2,418,932 4/1947 Harr 204/38 C FOREIGN PATENTS OR APPLICATIONS 446,546 2/1948 Canada 204/38 [451 Nov. 20, 1973 674,490 6/1950 Great Britain 204/38 Primary Examiner-John H. Mack Assistant Examiner-R. L. Andrews AttorneyWalter Becker [5 7 ABSTRACT A multi-stage method of providing work pieces, especially bands, strips, and sheets with a layer of enamel, according to which the work piece to be enameled is degreased and subsequently subjected to a plurality of treatment steps with a rinsing step being effected after each treatment step, said method including descalin the work piece in a nitric acid of from 3 to 8 percent by volume, electrodepositing from at least one electrolyte bath within a temperature range of from room temperature to 80C upon the thus treated work piece a metallic layer containing iron and at least one of the metals, nickel, cobalt and manganese, in which at least one of the metals nickel, cobalt and manganese up to a total concentration of from 50 grams per liter of these foreign metals, posttreating the work piece in an acid within a time period of from 10 to 20 seconds, and subsequently enameling the work piece.

14 Claims, N0 Drawings METHOD OF ENAMELING STRIPS AND SHEETS OF STEEL The present invention relates to a multi-stage method of one-layer enameling steel bands and steel sheets according to which the bands, strips or sheets are degreased, are rinsed in cold water between each method step and after an intermediate treatment are enameled.

Methods of one-layer enameling steel sheets, in other words methods which do not employ a base enamel, have been known. According to one of these known methods described in British Pat. No. 763,379, the metal sheet to be enameled is first electrolytically degreased and after a rinsing in water is chemically or electrolytically pickled in sulfuric acid or in a mixture of formic acid and nitric acid and is again rinsed. Following the pickling step, the metal sheet is plated electrolytically in a nickel bath with nickel and subsequently is enameled. If the enameling is not carried out shortly after the nickel plating step, the nickel-plated metal sheet is electrolytically coated with a zinc coat which is removed prior to the enameling step. However, this method does not yield a sufficient adherence of the enamel coat to the steel sheet.

According to a further heretofore known method for enameling metal sheets as described in German Patent No. 828,626, it is likewise suggested to electroplate the metal sheet with nickel which is annealed in an oxidizing manner and is subsequently pickled. Instead of nickel, according to German Auslegeschrift 1,017,876, also cobalt or a mixture of nickel and cobalt may be employed. The oxidizing annealing at relatively high temperatures and the subsequent cooling in a precisely determined atmosphere is rather costly so that also this known method is not satisfactory.

It is, therefore, an object of the present invention to provide a method of one-layer enameling bands, strips and sheets, which will overcome the above mentioned drawbacks.

It is another object of this invention to provide a method as set forth in the preceding paragraph, which in a particularly simple manner will reduce the treatment time and which will lend itself to a continuous treatment of strips, bands or sheets of steel, while steel sheets and bands or strips with a normal carbon content and also steel sheets, strips and bands which have previously been decarbonized can be covered with a proper and well adhering enamel coat.

The above outlined objects have been realized by the method according to the present invention which is characterized primarily in that the band, strip or sheet is descaled chemically or anodically in a 3 to 8 volume percent nitric acid, and is furthermore characterized in that upon the thus prepared band, strip or sheet there is deposited a metallic layer of iron and one or two of r the metals nickel, cobalt and manganese which layer is cathodically electrodeposited from one or more electrolytic baths at a temperature within the range of from room temperature to 80C, said layer being adapted in wet condition to be wiped off. The method according to the present invention is furthermore characterized in that one or two of the metals nickel, cobalt, manganese are added to the electrolyte up to a total concentration of 50 grams per liter of these foreign metals. The band, strip or sheet is chemically or anodically posttreated in an acid over a period of from 10 to a maximum of seconds. Subsequently, the thus treated material is a rectilinear or branch linked aliphatic hydrocarbon residue with from 1 to 6 carbon atoms, and- /or bb. a methacrylate the ester group of which consists of an aliphatic straight linked or branch linked hydrocarbon residue with from 1 to 6 carbon atoms,

are linked to each other in a polymeric manner;

b. l to 98 percent by weight of another film-forming binder which is compatible with the component a) of the group of the cumarone resins and/or of the ketone resins, if desired in combination with a hydrated abietyl alcohol,

c. 1 to 40 percent by weight of a benzene dicarboxylic acid ester,

said lacquer or enamel following the stoving being deformable and at the temperatures employed during the enameling step depolymerizes completely and without residues by volatilization while the enamel frits melt into a unitary coat or cover on the band or sheet.

According to a preferred embodiment of the invention, the lacquer or enamel with reference to the solid body comprises as essential ingredientsthe following components:

a. From to 92 percent by weight of an acrylic re sin(Acrylatharz) polymer the structural constituents of which consist of a methacrylate the ester group of which consists of an aliphatic straight linked or branch linked hydrocarbon residue with from 1 to 6 carbon atoms in polymeric interlinked connection,

b. from 3 to 20 percent by weight of another film forming binder compatible with the component a) supra and selected from the group of cumarone resins and/or ketone resins, if desired, in combination with a hydrated abietyl alcohol,

0. from 5 to 20 percent by weight of a benzene dicarboxylic acid ester.

It has been found expedient in this connection to stove the coat at a temperature of from 150 to 350C over a period of from 30 minutes to l5 seconds, and to carry out the depolymerization at temperatures from 500C on, preferably from 700C on.

For the abovereferred to descaling treatment, it is advantageous, depending on the successive method steps, chemically to descale the strip, band or sheet in' nitric acid of from 3 to 8 percent by volume at room temperature for a period of from 30 to 60 seconds, or to descale the strip, band or sheet anodically in nitric acid of from 3 to 8 percent by volume at a current density of from 10 amperes per square decimeter at room temperature for a period of about 10 seconds. In an expedient manner, a quantity of from 10 percent by volume of sulfuric acid may be added to the bath, or the bath may during an anodic descaling at a temperature of from 40 to C consist merely of a sulfuric acid of 10 percent by volume.

For purposes of applying the metallic layer adapted to be wiped off, various embodiments are possible. According to a preferred manner, following the descaling step, upon the strip, band or sheet there is from an electrolyte containing a bivalent iron, iron electrodeposited at a current density of from 5 to amperes per square decimeter within a period of from 10 to 30 seconds. Subsequently, from a nickel electrolyte, for instance of the Watt type or the citric acid type, nickel is cathodically electrodepositedat a current density of from 3 to l0 amperes per square decimeter in a period of from 6 to seconds. However, in a corresponding manner, instead of employing a nickel electrolyte, also a cobalt containing sulfate electrolyte may be employed in which instance the cobalt is electrodeposited onto the strip, band or sheet at a current density of from 3 to 10 amperes per square decimeter in a period of from 6 to 15 seconds. If in addition to iron, advantageously and simultaneously at least one or at best two metals are to be electrodeposited, it is suggested that from an electrolyte which contains bivalent iron and simultaneously one or two of the metals manganese in a quantity of from 1 to grams per liter as manganese sulfate, nickel in a quantity of from 10 to 50 grams per liter, and cobalt in a quantity of from 10 to 50 grams per liter, the said metals be electrodeposited upon the strip, band or sheet at a current density of from 5 to 20 amperes per square decimeter in a period of from 10 to 30 seconds.

For the chemical posttreatment of the strips, bands or sheets provided with the metallic layer, the respective strip, band or sheet is advantageously immersed in a nitric acid of from 3 to 8 percent by volume at room terperature for a period of from 5 to 20 seconds whereas, with an anodic posttreatment in a sulfuric acid of 10 percent by volume, a current density of 10 amperes per square decimeter at a room temperature of from 40 to 80C and a treatment time of approximately 10 seconds will be required.

The advantages of the method according to the present invention are seen primarily in the fact that in a simple manner a continuous relatively short treatment of strips, bands and sheets is possible, and that this is possible for steel strips, bands and sheets with a normal carbon content of from 0.04 to 0.10 percent and also with a very low carbon content of from 0.006 percent. With this method, very adherent enamel layers can be produced on such strips, bands or sheets. In the same manner in which a treatment of strips, bands and sheets can be carried out according to the above outlined method of the invention, it is also possible advantageously to use this method in connection with the treatment of individual pieces.

The method according to the present invention of providing steel strips, bands or sheets with one-layer enameling will now be described in more detail in connection with particular successful examples.

EXAMPLE I l. Anodic degreasing in soda lye at a temperature of from 80C and at a current density of 15 amperes per square decimeter in a period of 6 seconds,

2. rinsing,

3. descaling at room temperature in a nitric acid of 5 percent by volume in a period of 30 seconds,

4. rinsing,

5. cathodic electrodeposition of iron, manganese and nickel from an electrolyte having the following composition:

grams per liter ferro sulfate 10 grams per liter manganese-(lI)-sulfate 100 grams per liter nickel sulfate 20 grams per liter nickel chloride 50 grams per liter magnesium sulfate 25 grams per liter ammonium sulfate 20 grams per liter boric acid, the pH-value of which is by means of sulfuric acid adjusted to 2.0 at a current density of 10 amperes per square decimeter, and at a temperature of 60 C. in the time period "of 10 seconds. Anode material: soft carbon steel,

6. rinsing,

7. posttreatment at room temperature in nitric acid of 5 percent by volume for a period of 20 seconds,

8. rinsing,

9. enameling.

EXAMPLE ll 1. Anodic degreasing in soda lye at a temperature of C., a current density of 15 amperes per square decimeter in a time period of six seconds,

2. rinsing,

3. descaling at room temperature in a nitric acid of 5 percent by volume in a period of 30 seconds,

4. cathodic electrodeposition of iron at room temperature from an electrolyte with the following composition: l40 grams per liter iron (ll) sulfate grams per liter magnesium sulfate 50 grams per liter ammonium sulfate,

the pH-value of which is adjusted by means of sulfuric acid to 2.0 at a current density of 10 amperes per square decimeter in a time period of 10 seconds. Anode material: soft carbon steel,

5. rinsing,

6. cathodic electrodeposition of cobalt at room temperature from an electrolyte with the following composition:

300 grams per liter cobalt sulfate 20 grams per liter sodium chloride 40 grams per liter boric acid, the pH-value of which is adjusted to 2.0 by means of sulfuric acid at a current density of 10 amperes per square decimeter in a time period of 10 seconds,

7. rinsing,

8. anodic posttreatment at 60 C. in sulfuric acid of 10 percent by volume and at a current density of 10 amperes per square decimeter in a time period of 10 seconds,

9. rinsing,

l0. enameling.

EXAMPLE Ill 1. Anodic degreasing in soda lye at a temperature of 80 C. and a current density of 15 amperes per square decimeter in a time period of six seconds,

2. rinsing,

3. descaling at room temperature in nitric acid of 8 percent by volume in a time period of 30 seconds,

4. rinsing,

5. cathodic electrodeposition of iron from an electrolyte with the composition:

grams per liter iron (ll) sulfate 100 grams per liter magnesium sulfate 50 grams per liter ammonium sulfate, the pH-value of which is by means of sulfuricacid adjusted to 2.0 at a current density of amperes per square decimeter and at room temperature in a time period of 10 seconds. Anode material: soft carbon steel,

6. rinsing,

7. cathodic electrodeposition of nickel from an electrolyte with the composition:

200 grams per liter nickel sulfate 50 grams per liter nickel chloride 40 grams per liter sodium citrate, the pH-value of which is by means of sulfuric acid adjusted to 2.0 at a current density of 6 amperes per square decimeter and at a temperature of 50 C. in a time. period of ,10 seconds,

8. rinsing,

.9. cathodic electrodeposition of zinc from an electrolyte of the composition: 320 grams per liter zinc sulfate 20 grams per liter ammonium chloride, the pH-value of which is by means of sulfuric acid adjusted to 2.0 at a current density of 30 amperes 'per square decimeter and at a temperature of 60 C. in a time period of 10 seconds, l0. rinsing and drying,

l l. zinc removal (of the sheets to be enameled) in nitric acid of 5 percent by volume at a room temperature in a time period of 20 seconds,

12. rinsing,

l3. enameling.

EXAMPLE IV A sheet strip belt or the like treated and dried in conformity with the method steps 1 to 8 of the preceding EXAMPLES l-lli has applied thereto in any standard manner for instance by painting, immersing, spraying, or rolling a lacquer having worked thereinto white or colored pigmented enamel frits in a quantity of from 50 to 80 percent by weight. The lacquer is applied in the form of a liquid mixture in organic solvent and with regard to the solid body contains as essential ingredients:

a. from 1 to 98 percent by weight of an acrylic resin polymer the structural constituents of which are linked to each other in a polymeric manner, said structural constituents being:

aa. an acrylate the ester group of which consists of a rectilinear or branch-linked aliphatic hydrocarbon residue with from one to six carbon atoms, and/or bb. a methacrylate the ester group of which consists of an aliphatic straight-linked or branch-linked hydrocarbon residue with from one to six carbon atoms.

b. from 1 to 98 percent by weight of another filmforming binder which is compatible with the component a)supra, of the group of the cumarone resins and/or ketone resins, if desired in combination with a hydrated abietyl alcohol,

c. from 1 to 40 percent by weight of a benzene dicarboxylic acid ester.

The coat of lacquer is subsequently at a temperature of from 150 to 350 C., preferably from 160 to 300 C., burned or stoved into the sheet strip or belt in a time period of from 30 minutes to seconds while at the mentioned lower temperatures, longer burning or stoving times and at the higher temperatures correspondinglyshorter burning or stoving times are to be employed. I

It may bezmentioned that the subsequent depolymerization of the lacquer components occurs over a range of temperature,"and that therefore the burning orstoving temperatures which preferably are by about 20 C. higher thanithemelting point of the inserted frits can'- not be increased at will. The lacquer film burned into the strip sheet or belt has a smooth, dull or mat, or nonglossy appearance while the color-"tone depends on the enamel frit worked into thefla cjquer. Theiburn'ed-in or stoved lacquer film is hard arid mechanic'ally resistant, especially against scratches, impacts and blows. In particular, the belt strip or sheet provided with the coat of lacquer is deformable and can be deep drawn so that no difficulties will be encountered in shaping the sheet strip or belttreated in the above mentioned manner in conformity with the desires of the respective manufacturer.

In a later stage of manufacture, the lacquer film is heated to a temperature of over approximately 500 C., preferably ata temperature over 700 C. on, depolymerized completely in a furnace and without residues while the lacquer ingredients are volatilized and the enamel frits melt to a uniform flawless enamel coat.

It is, of course, to be understood that the present invention is, by no means, limited to the specific examples set forth above but also comprises any modifications within the scope of the appended claims.

What we claim is:

l. A multi-stage method of providing work pieces of steel with a single layer of enamel, according to which the work piece to be enameled isdegreased and subsequently subjected to a plurality of treatment steps with a rinsing step effected after each treatment step, said method including the steps of: acid treating the workpiece for neutralizing and oxidizing in a nitric acid solution of from 3 to 8 percent by volume for a short time, electrodepositing upon the thus treated work piece a spongy metallic layer containing iron and at least one of the foreign metals selected from the group consisting of nickel, cobalt, and manganese from an electrolyte containing at least one of the metals of the group consisting of nickel, cobalt and manganese up to a total concentration of 50 grams per liter of these foreign metals and within a temperature range of from room temperature to C, post-treating the workpiece in an acid, and subsequently enameling the workpiece.

2. A method in combination according to claim 1, in which the post-treatment in an acid is effected chemically.

3. A method in combination according to claim 2, which includes the step of chemically post-treating the metallic layer coated work piece in a nitric acid of from 3 to 8 percent by volume within a time period of from 5 to 20 seconds.

4. A method in combination according to claim 1, in which the post-treatment in an acid is effected anodically.

5. A method in combination according to claim 4, which includes the step of anodically post-treating the metallic layer covered work piece in sulfuric acid of about 10 percent by volume at a current density of 10 A/dm at a temperature of from 40 to 80C for a time period of approximately 10 seconds.

6. A method in combination according to claim 1, which includes the step of chemically acid treating the work piece in a nitric acid solution of from 3 to 8 percent by volume at room temperature within a time period of from 30 to 60 seconds.

7. A method in combination according to claim 1, which includes the step of anodically descaling the work piece in a nitric acid solution of from 3 to 8 percent by volume at a current density of about 10 amperes per square decimeter and at room temperature for approximately 10 seconds.

8. A method in combination according to claim 7, which includes the step of adding sulfuric acid of approximately 10 percent by volume to the descaling bath.

9. A method in combination according to claim 8, in which the descaling bath for purposes of anodically acid treating consists of sulfuric acid of about 10 percent by volume.

10. A multi-stage method of providing work pieces of steel with a layer of enamel, according to which the work piece to be enameled is degreased and subsequently subjected to a plurality of treatment steps with a rinsing step effected after each treatment step, said method including the steps of acid treating the work piece for neutralizing and oxidizing in a nitric acid solution of from 3 to 8 percent by volume, electrodepositing upon the thus treated work piece a spongy metallic layer containing iron and at least one of theforeign metals selected from the group consisting of nickel, cobalt and manganese, from an electrolyte containing at least one of the metals of the group consisting of nickel, cobalt and manganese up to a total concentration of 50 grams per liter of these foreign metals and within a temperature range of from room temperature to 80C, post-treating the work piece in an acid, drying the thus treated work piece, applying to the thus treated work piece a coat of lacquer having distributed therein enamel frits, said lacquer being applied in the form of a liquid mixture in an organic solvent which with regard to the solid body contains as essential components a. from 1 to 98 percent by weight of an acrylic resin polymer the structural constituents of which are interlinked in a polymeric manner and comprise at least one of the following two acrylates:

aa. an acrylate the ester group of which consists of an aliphatic hydrocarbon residue with from one to six carbon atoms and bb. a methacrylate the ester group of which consists of an aliphatic hydrocarbon residue with from one to six carbon atoms;

b. from 1 to 98 percent by weight of another filmforming binder which is compatible with said component (a) and is of at least one of the groups of the cumarone resins and the ketone resins;

c. from 1 to 40 percent by weight of benzene dicarboxylic acid ester.

11. A method in combination according to claim 10, in which said lacquer has white enamel frits distributed therein.

12. A method in combination according to claim 10, in which said lacquer has colored enamel frits distrib uted therein.

13. A method in combination according to claim 10, in which said lacquer with regard to the solid body comprises:

a. from to 92 percent by weight of an acrylic resin polymer the structural constituents of which consist of a methacrylate the ester group of which consists of an aliphatic hydrocarbon residue with from l to 6 carbon atoms in polymeric interlinked relationship;

b. from 3 to 20 percent by weight of another filmforming binder compatible with said component (a) and selected from the group consisting of cumarone resins and ketone resins; and

c. from 5 to 20 percent by weight of a benzene dicarboxylic acid ester.

14. A method according to claim 10, which includes the step of curing said coat of lacquer within a temperature range of from C to 300C within a time period of from 30 minutes to 15 seconds and carrying out the depolymerization at a temperature of at least 500C. 

2. A method in combination according to claim 1, in which the post-treatment in an acid is effected chemically.
 3. A method in combination according to claim 2, which includes the step of chemically post-treating the metallic layer coated work piece in a nitric acid of from 3 to 8 percent by volume within a time period of from 5 to 20 seconds.
 4. A method in combination according to claim 1, in which the post-treatment in an acid is effected anodically.
 5. A method in combination according to claim 4, which includes the step of anodically post-treating the metallic layer covered work piece in sulfuric acid of about 10 percent by volume at a current density of 10 A/dm2 at a temperature of from 40* to 80*C for a time period of approximately 10 seconds.
 6. A method in combination according to claim 1, which includes the step of chemically acid treating the work piece in a nitric acid solution of from 3 to 8 percent by volume at room temperature within a time period of from 30 to 60 seconds.
 7. A method in combination according to claim 1, which includes the step of anodically descaling the work piece in a nitric acid solution of from 3 to 8 percent by volume at a current density of about 10 amperes per square decimeter and at room temperature for approximately 10 seconds.
 8. A method in combination according to claim 7, which includes the step of adding sulfuric acid of approximately 10 percent by volume to the descaling bath.
 9. A method in combination according to claim 8, in which the descaling bath for purposes of anodically acid treating consists of sulfuric acid of about 10 percent by volume.
 10. A multi-stage method of providing work pieces of steel with a layer of enamel, according to which the work piece to be enameled is degreased and subsequently subjected to a plurality of treatment steps with a rinsing step effected after each treatment step, said method including the steps of acid treating the work piece for neutralizing and oxidizing in a nitric acid solution of from 3 to 8 percent by volume, electrodepositing upon the thus treated work piece a spongy metallic layer containing iron and at least one of the foreign metals selected from the group consisting of nickel, cobalt and manganese, from an electrolyte containing at least one of the metals of the group consisting of nickel, cobalt and manganese up to a total concentration of 50 grams per liter of these foreign metals and within a temperature range of from room temperature to 80*C, post-treating the work piece in an acid, drying the thus treated work piece, applying to the thus treated work piece a coat of lacquer having distributed therein enamel frits, said lacquer being applied in the form of a liquid mixture in an organic solvent which with regard to the solid body contains as essential components a. from 1 to 98 percent by weight of an acrylic resin polymer the structural constituents of which are interlinked in a polymeric manner and comprise at least one of the following two acrylates: aa. an acrylate the ester group of which consists of an aliphatic hydrocarbon residue with from oNe to six carbon atoms and bb. a methacrylate the ester group of which consists of an aliphatic hydrocarbon residue with from one to six carbon atoms; b. from 1 to 98 percent by weight of another film-forming binder which is compatible with said component (a) and is of at least one of the groups of the cumarone resins and the ketone resins; c. from 1 to 40 percent by weight of benzene dicarboxylic acid ester.
 11. A method in combination according to claim 10, in which said lacquer has white enamel frits distributed therein.
 12. A method in combination according to claim 10, in which said lacquer has colored enamel frits distributed therein.
 13. A method in combination according to claim 10, in which said lacquer with regard to the solid body comprises: a. from 70 to 92 percent by weight of an acrylic resin polymer the structural constituents of which consist of a methacrylate the ester group of which consists of an aliphatic hydrocarbon residue with from 1 to 6 carbon atoms in polymeric interlinked relationship; b. from 3 to 20 percent by weight of another film-forming binder compatible with said component (a) and selected from the group consisting of cumarone resins and ketone resins; and c. from 5 to 20 percent by weight of a benzene dicarboxylic acid ester.
 14. A method according to claim 10, which includes the step of curing said coat of lacquer within a temperature range of from 160*C to 300*C within a time period of from 30 minutes to 15 seconds and carrying out the depolymerization at a temperature of at least 500*C. 